1. Field of the Invention
The present invention relates generally to wireless communication systems, and more particularly to a system for use in deep underground mines to track and monitor personnel and equipment, and to provide wireless two-way communications for day-to-day miner safety enhancement and for rescue operations.
2. Discussion of Related Art
There are numerous risks inherent in underground mining operations: fire, cave-in, methane or coal-dust explosion, flooding, asphyxiation, and so forth. When miners are trapped, the success of rescue operations depends upon the rapidity and the efficiency of the rescue response. Both would be greatly enhanced if mining operators implemented a suitable underground communications and personnel tracking system.
There are numerous difficulties in using the current location-finding devices in an underground environment. GPS technology simply does not work. GPS satellites transmit low power radio signals, denominated L1 and L2. The L1 frequency is for civilian GPS systems and operates at 1575.42 MHZ in the UHF band. However, the signals are line-of-sight, and though they can pass through clouds and generally transparent materials, they will not penetrate solid objects such as buildings and earth.
Moreover, there are numerous challenges in using wireless communications generally for underground use. Until the present, there has not existed a wireless communication system capable of functioning as a backhaul method in underground environments. And it is difficult to use radio frequency propagation devices in underground environments as the basis for an accurate location algorithm because underground environments tend to block signals, cause multipath fading, co-interference, hardware/package degradation, environmental damage due to dust, water, and the like. Further, there are difficulties in implementing large-scale distributed wireless networks and hybrid wired/wireless networks in underground environments, especially given the generally linear and labyrinthine configurations of most tunnel and mine structures, and due to the presence of signal blocking machinery. Moreover, there are the challenges in achieving the following objectives: (1) acceptable “location update rate” performances with large-scale mine footprints having a large number of miners across low bandwidth backhaul networks (e.g. existing long-haul RS485 at 2400 bps); (2) providing a system requiring only a low power demand suitable for all-battery operation in some areas; (3) adequate fault-tolerance for a solution aimed at protecting/saving human life, especially where the deployment environment is harsh and hazardous; and (4) sufficient portability and rapid deployment characteristics needed in emergency rescue scenarios.